An apparatus that detects faint light has widely been introduced mainly in the medical and research fields in recent years. In such an apparatus, a photomultiplier tube, which is relatively expensive, is used as a detection unit of faint light in many cases.
Moreover, an apparatus is also proposed which detects faint light using an imaging device such as a CMOS (Complementary Metal Oxide Semiconductor) image sensor, which can be manufactured at low cost, instead of the photomultiplier tube (see, for example, Patent Document 1).